The invention relates to a method for determination of strain distribution in components, in particular in gas turbine components.
If a strain distribution is supposed to be determined for a component, the procedure for doing so is either purely experimental or purely analytical according to the prior art. Using strain gauges that are positioned on the component and provide measured values about the strain distribution during vibrational excitation of the component is cited as an experimental procedure known from the prior art for determining the strain distribution of a component. However, these types of strain gauges can provide only a few local measured values for strain distribution of a component. Reference is made to the finite-element method as an analytical procedure known from the prior art for determining the strain distribution of a component. The finite-element method represents a purely mathematical determination of the strain distribution and does not take actual component geometries into consideration.
Starting herefrom, the present invention is based on the objective of creating a novel method for determination of the strain distribution in components, in particular in gas turbine components.
According to the invention the method is comprised of at least the following steps: a) production of a component, the strain distribution of which is to be determined; b) vibrational excitation of the component and measured recording of a vibrational amplitude distribution of the component for a number of measured points by means of a vibrometer, each measuring point being determined by three coordinates and the measured vibrational amplitude distribution of each measuring point being a vectorial parameter; c) smoothing of the vibrational amplitude distribution recorded by measurement for each measuring point; d) definition of polygonal elements, wherein each measuring point forms a corner of at least one element; e) calculation of a tensor strain condition for each of the polygonal elements from the vectorial vibrational amplitude distributions present in the corners of the elements and f) calculation of the strain distribution in the corners of the elements from the strain conditions of the elements.
The inventive method for determination of the strain distribution of a component represents a combination of experimental and analytical procedures. A vibrometer is used to measure the vibrational amplitude distributions on an actual component and consequently taking the actual component geometry into consideration, preferably for different modes of the component. Then analytical calculation is used to determine the strain distribution of the component from these experimental measuring data in the form of a tensor, in particular vectorial, strain condition. This represents a completely new procedure for determining the strain distribution in components.
According to an advantageous development of the invention, the measuring points in component regions with higher strain gradients are distributed over the component at a smaller distance than in component regions with lower strain gradients, wherein, to do so, the distribution of the measuring points over the component is performed iteratively.
The smoothing of the vibrational amplitude distribution recorded by measurement for each measuring point is preferably performed with the aid of cubic spline smoothing.
According to another advantageous development of the invention, for the calculation of the strain distribution, the tensor strain conditions of the elements, which are present in a local coordinate system of the respective element, are converted by a transformation on the main axes of the local coordinate system of the respective element to scalar main strains, wherein, in addition, to calculate the strain distribution for the corners of the elements, the scalar main strains in the respective corners are averaged, wherein a scalar strain distribution for the corners of the elements is produced as the result. Alternatively, for the calculation of the strain distribution, the tensor strain conditions of the elements, which are present in a local coordinate system of the respective element, are transformed to a global coordinate system, wherein, in addition, to calculate the strain distribution for the corners of the elements, the transformed, tensor strain conditions in the respective corners are averaged, wherein a tensor strain distribution for the corners of the elements is produced as the result.
Preferred developments of the invention are yielded from the subsequent description. Without being limited hereto, exemplary embodiments of the invention are explained in greater detail in the following.